Chapter 1 - Activity and Diversity of Aerobic Methanotrophs in Thermal Springs of the Russian Far East

Abstract

Terrestrial hot springs are heterogeneous both biogeochemically and spatially, occur in various environments, and are distributed widely over the world. Microbial species are diverse in hot springs and their ecological functions are not completely known; thus, the role of hydrotherms in global biogeochemical cycling and the preservation of ancient metabolic forms are difficult to precisely interpret. Methane-oxidizing bacteria (MOB), or methanotrophs, share the unique ability to use methane, the second most important greenhouse gas, as the sole carbon and energy source. The Russian Far East is one of the most active in the world terrestrial geothermal area, but until now very limited data have been available for CH4 oxidation in this region and the existence and activity of thermophilic methanotrophs have been questioned. This chapter, firstly to our knowledge, synthesizes the environmental and climatic factors influencing methane consumption regarding activity and diversity of methanotrophic communities in the geothermal springs of Russian Far East, specifically the Kamchatka Peninsula and Kunashir Island. It was shown that all studied samples contained the dissolved methane and methane oxidation was recorded by a radioisotope tracer technique in the major part of the studied hot springs. Molecular analysis revealed that methanotrophic diversity in these springs was rather low and did not exceed 2–3 genera per spring. Among the hottest samples (50–90°C), thermophilic members of the Gammaproteobacteria genus Methylothermus dominated, while some others are dominated by methanotrophs closely related to Methylomonas, Methylobacter, and Methylocystis. These results suggest that diverse methanotroph groups are adapted to hot springs, including the Methylomonas-Methylobacter and Methylocystis group, which has previously only been detected in cooler sites and the diversity of methanotrophs in thermal ecosystems is broader than previously suggested. So, monitoring and process understanding of CH4 consumption in these ecosystems is required to estimate global greenhouse gases balance and the contribution to global warming. Results from this chapter will provide novel insights into understanding the behavior of thermophilic microbial communities and will broaden our view of the importance of hydrothermal systems in the evolution of life and global chemical cycling.